Prosthetic and orthotic devices help restore mobility to people who lack able-bodied motion. Prosthetic devices are intended to replace the appearance of a missing limb or portion of a limb and can return mobility to the wearer or user. Orthotic devices are intended to support or supplement an existing limb, by assisting with movement, reducing weight-bearing loads on the body, reducing pain, and increasing endurance. Prosthetic and orthotic devices are available to replace or support various portions of the body. Lower limb prosthetic devices include a prosthetic foot, foot-ankle prosthesis, prosthetic knee joint, and prosthetic hip joint. Lower limb orthotic devices include a foot orthoses, ankle-foot orthoses, knee-ankle-foot orthoses, and knee orthoses. People who require a lower limb prosthesis or orthosis often expend more metabolic power to walk or move at the same speed as able-bodied individuals.
Human locomotion, such as walking and running, is commonly described in terms of gait. Gait is a cyclical pattern of leg and foot movement that creates locomotion. A gait cycle is defined for a single leg and begins with the initial contact of the foot with the ground or heel strike. The conclusion of a gait cycle occurs when the same foot makes a second heel strike. The gait cycle can be divided into two phases, stance phase and swing phase. Stance phase begins with heel strike and ends when the toe of the same foot leaves the ground. Swing phase begins when the foot leaves contact with the ground and ends with the heel strike of the same foot. One goal of lower limb prosthetic and orthotic devices is to help the user achieve a normal gait, while reducing energy expended by the user.
Most if not all control systems for prosthetic and orthotic devices have focused on gait and other cyclical patterns of motion. Yet, humans spend a considerable portion of the day involved in non-gait activities, while wearing the prosthetic or orthotic device. For example, the person may slide foot position or cross legs while sitting in a chair, or change balance point while leaning against a bar or podium, or shift stance while standing in a social gathering. The person may be engaged in random, complex, non-cyclic activities, such as dancing, exercise routines, or sporting activities, while wearing the prosthetic or orthotic device. The person may be wearing long pants or long dress that covers the prosthetic or orthotic device. In any case, the person likely prefers the non-gait activity while wearing the prosthetic or orthotic device to appear as natural as possible, without indicating, revealing, or otherwise drawing attention to the presence of the prosthetic or orthotic device. The non-gait activity should appear as biological motion, without an artificial or mechanical appearance.